code: def mean_absolute_error(
      pred_dist: MultivariateNormal,
      test_y: torch.Tensor,
  ):
      """
      Mean absolute error.
      """
      combine_dim = (
          -2
          if isinstance(pred_dist, MultitaskMultivariateNormal)
          else -1
      )
      return torch.abs(pred_dist.mean - test_y).mean(dim=combine_dim)
  
file_path: gpytorch/gpytorch/metrics/metrics.py
imports: from math import pi
  from typing import Optional
  import torch
  from ..distributions import MultitaskMultivariateNormal, MultivariateNormal
label_desc: Use image node_id 1 for calling a global function with example usage: mean_absolute_error(pred_dist, test_y) and returns: torch